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737-300/400/500MAINTENANCE MANUAL
LANDING GEAR CONTROL SYSTEM - DESCRIPTION AND OPERATION
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General
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A. The landing gear control system is operated by moving a control lever projecting from the pilots' instrument panel (Fig. 1). A cable system transmits the control lever movement to a selector valve in the left wheel well. When positioned by the control lever, the selector valve directs hydraulic pressure to the actuators for gear retraction and extension. The control lever is provided with a lock to prevent the lever from being moved into UP position when the airplane is supported on the gear. An override trigger in the control lever may be used to bypass the lock for testing or if the lock system should lose electrical power.
Landing Gear Selector Valve
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A. The landing gear selector valve directs hydraulic pressure to the landing gear up and down lines (Fig. 2). Return fluid from the landing gear system passes back through the selector valve and on to the hydraulic system A reservoir. The selector valve is bolted to the ceiling of the left main wheel well. Linkage connects the selector valve to the control cable system. When the landing gear control handle is operated, motion from the handle is transferred through the cable system to a shaft passing through the wheel well ceiling. An arm on the end of shaft below the ceiling positions the selector valve through an adjustable link.
Landing Gear Control Cable System
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A. The landing gear control cable system transfers movement from the control lever to the landing gear selector valve (Fig. 1). The control cable system consists of four cables, two short and two long. Short cables run forward and down from the control lever drum, then aft under the control cabin floor. Long cables run forward from the selector valve control drum to meet the control lever cables at a point under the control cabin floor where the cables are joined by turnbuckles.
Landing Gear Control Lever
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A. The landing gear control lever runs in a guide as the lever is moved up or down. The guide has detents to hold the control lever in any one of three positions, UP, OFF, or DN. To change the control lever position, it is necessary to pull out the lever to release a roller on the inner end from the detent.
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A 737-300/400/500MAINTENANCE MANUAL
LANDING GEAR LANDING GEAR SELECTOR VALVE CONTROL LEVER
CONTROL CABLES
GEAR UP CONTROL CABLE LGVA
TURNBUCKLES QUADRANT
GEAR DOWN CONTROL CABLE LGVB
TURNBUCKLE QUADRANT SUPPORT BRACKET
GEAR UP DETENT CONTROL LEVER POSITION SWITCH GEAR OFF DETENT CONTROL LEVER DRUM PRESSURE PORT RETURN PORT DOWN PORT UP PORT
GEAR DOWN CONTROL CABLE LGVB CONTROL LEVER LOCK OVERRIDE TRIGGER CONTROL LEVER (GEAR DOWN POSITION) LANDING GEAR LANDING GEAR SELECTOR VALVE
GEAR UP CONTROL CABLE LGVA LOCK SOLENOID
Figure 1 Landing Gear Control Component Location
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A 737-300/400/500MAINTENANCE MANUAL
DOWN LINE UP LINE
RETURN LINE PRESSURE LINE
OFF POSITION
GEAR UP
Landing Gear Selector Valve Schematic
Figure 2
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A
737-300/400/500MAINTENANCE MANUAL
B. The lock override mechanism enables the inner end of the control lever to be pulled clear of the lock stop when the control lever lock is engaged. The override feature is obtained by making the control lever shaft in two parts, one sliding inside the other. A trigger connected to the inner part projects through a slot in the underside of the outer shaft. A compression spring between a flange on the inner shaft and the control handle quadrant holds the trigger against the bottom of the slot (Fig. 3). When the control lever is pulled, both the inner and outer shafts move together through the quadrant until the inner end clears the detent. At this point, a stop prevents further movement. To retract the inner end of the lever far enough to pass the lock stop, the trigger must be operated. Pulling the trigger telescopes the inner shaft into the lever, the additional retraction of the control lever inner end thus obtained, allows the lever to clear the lock stop.
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本文链接地址：737-300 400 500 AMM 飞机维护手册 起落架 LANDING GEAR 2(46)
